The image may look completely normal, as it appears to contain thousands of stars, but it is actually supermassive black holes. Surprisingly, it is a map of the sky showing more than 25,000 supermassive black holes. Each black hole is located in a different distant galaxy.
An international group of astronomers published in early 2021 in the journal Astronomy and astrophysics, a map of the sky showing 25,000 black holes, ranked as the most detailed ever in the so-called low radio frequency field. The map is the result of 256 hours of observations of the northern sky, using data from the Low Frequency Array (LOFAR) over Europe. The interferometry network consists of about 20,000 radio antennas, spread over 52 stations spread over nine European countries.
“This is the result of many years of working with very challenging data. We had to devise new ways to convert radio signals into images of the sky.” He said in a statementDirector of the investigation Francesco de Gasperin.
Currently, louvre It is the largest radio telescope operating at the lowest frequencies that can be observed from Earth. Unlike monocular telescopes, LOFAR is a multipurpose network of sensors, with an innovative network and computing infrastructure that can handle extremely large amounts of data.
Since this is not a space telescope, but rather makes its observations from the surface, it has significant challenges to overcome. The main factor is the ionosphere that surrounds the Earth – a layer of free electrons that clouds telescopes – making black holes difficult to track.
“It’s similar to trying to see the world while you are immersed in a swimming pool. When you look up, the waves in the pool water deflect rays of light and distort your vision.” explain Co-author Reinout van Weeren (Leiden Observatory).
The frequencies that penetrate the ionosphere can vary depending on atmospheric conditions. In order to successfully complete the mission, the team used supercomputers running algorithms to correct for ionospheric interference every four seconds. During the 256 hours that LOFAR has been observing the sky, there have been many corrections.
When you hear “25,000 supermassive black holes,” the possibilities are many and a lot of space comes to mind, and that’s what happens. However, the map covers only 4% of the northern half of the sky. The astronomers plan to continue until they map the entire northern sky. In addition to supermassive black holes, the map also provides information about the large-scale structure of the universe, among other things.
Additional investigations may allow study of more than 1 million low-frequency radio spectrum, providing unique insights into physical models of galaxies, active nuclei, galaxy clusters, and other areas of research. “This experiment represents a unique attempt to explore the extremely low-frequency sky with high resolution and angular depth,” they wrote Article authors.
The study was detailed in an article published in Astronomy and astrophysics.
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